Emergence of XDR-TB

WHO concern over extensive drug resistant TB strains that are virtually untreatable

5 September 2006 | Geneva -The World Health Organization (WHO) has expressed concern over the emergence of virulent drug-resistant strains of tuberculosis (TB) and is calling for measures to be strengthened and implemented to prevent the global spread of the deadly TB strains. This follows research showing the extent of XDR-TB, a newly identified TB threat which leaves patients (including many people living with HIV) virtually untreatable using currently available anti-TB drugs.

Later this week, WHO will join other TB experts at a two-day meeting in South Africa (7-8 September) to assess the response required to critically address TB drug resistance, particularly in Africa, and will take part in a news conference scheduled for Thursday, 7 September in Johannesburg.

What is XDR-TB?

MDR-TB (Multidrug Resistant TB) describes strains of tuberculosis that are resistant to at least the two main first-line TB drugs - isoniazid and rifampicin. XDR-TB, or Extensive Drug Resistant TB (also referred to as Extreme Drug Resistance) is MDR-TB that is also resistant to three or more of the six classes of second-line drugs.

The description of XDR-TB was first used earlier in 2006, following a joint survey by WHO and the US Centers for Disease Control and Prevention (CDC).

Resistance to anti-TB drugs in populations is a phenomenon that occurs primarily due to poorly managed TB care. Problems include incorrect drug prescribing practices by providers, poor quality drugs or erratic supply of drugs, and also patient non-adherence.

What is the current evidence of XDR-TB?

Recent findings from a survey conducted by WHO and CDC on data from 2000-2004 found that XDR-TB has been identified in all regions of the world but is most frequent in the countries of the former Soviet Union and in Asia.

In the United States, 4% of MDR-TB cases met the criteria for XDR-TB.

In Latvia, a country with one of the highest rates of MDR-TB, 19% of MDR-TB cases met the XDR-TB criteria.

Separate data on a recent outbreak of XDR-TB in an HIV-positive population in Kwazulu-Natal in South Africa was characterized by alarmingly high mortality rates.

Of the 544 patients studied, 221 had MDR-TB. Of the 221 MDR-TB cases, 53 were defined as XDR-TB. Of the 53 patients, 44 had been tested for HIV and all were HIV-positive.

52 of 53 patients died, on average, within 25 days including those benefiting from antiretroviral drugs.

Scarce drug resistance data available from Africa indicate that while population prevalence of drug resistant TB appears to be low compared to Eastern Europe and Asia, drug resistance in the region is on the rise.

Given the underlying HIV epidemic, drug-resistant TB could have a severe impact on mortality in Africa and requires urgent preventative action.

What action is required to prevent XDR-TB?

XDR-TB poses a grave public health threat, especially in populations with high rates of HIV and where there are few health care resources. Recommendations outlined in the WHO Guidelines for the Programmatic Management of Drug Resistant Tuberculosis include: